In a float glass manufacturing plant, a continuous float glass ribbon is produced. After the ribbon is sufficiently cooled or annealed, it is cut both transversely and longitudinally to form glass sheets of predetermined sizes. The longitudinal cutting, sometimes referred to as "slitting", is generally performed by glass cutting assemblies, supported transversely across the path of travel of the glass ribbon.
U.S. Pat. No. 3,834,258 issued to Ernst Zumstein, teaches an apparatus having a plurality of cutting assemblies mounted to carrier units which are displaceable, by a pusher rod driven by a stepper motor, along a guide rail extending transversely across a work surface which supports a plate of glass to be cut. The individual carrier units are connected through disengageable clutches with the pusher rod at preset distances from one another. Each carrier unit has friction braking means actuatable for generating a braking force greater than the holding force of the clutch which holds the carrier unit to the pusher rod, to thereby disengage the clutch and hold the carrier unit to the guide rail at a preselected location across the work surface. After all of the carrier units are positioned, their associated cutting assemblies can be actuated to longitudinally cut or score the glass plate. A disadvantage with the apparatus taught in U.S. Pat. No. 3,834,258 is that the individual carrier units and their associated cutting assemblies operate in individual, non-overlapping zones. This unduly restricts the longitudinal cutting pattern which can be imposed on the glass plate. For example, this presents a problem when narrow faults extend longitudinally through a glass sheet, e.g. near the edge(s) thereof, where it is desirable to have cutting assemblies which can be operated relatively close together in the same zone for cutting out the narrow fault. Further, to minimize lost production time it is desirable to be able to move a cutting assembly into the position of a worn-out or malfunctioning cutting assembly while it is being replaced or repaired. For these reasons, a positioning apparatus wherein the cutter assemblies are limited to movement within fixed, non-overlapping zones is disadvantageous.
U.S. Pat. No. 4,170,159, issued to Paul McNally, teaches a linear positioning apparatus which overcomes the above-delineated disadvantages of the Zumstein positioning apparatus. McNally, in his patent, teaches a movable carriage which is connected to a smooth actuating rod for movement therewith to a desired position where it is locked to a fixed bridge, permitting the actuating rod to move with respect thereto. The movable carriage is clamped to the actuating rod with a continual friction force which is easily overcome by the force with which the carriage is locked to the fixed bridge. When more than one carriage is utilized, adjacent carriages can be moved close together. Otherwise stated, movement of the carriages is not restricted to preselected zones. Positioning of the carriages is computer controlled. The positions of all carriages are stored and a carriage can be moved to a new position without returning to a fixed home position. This permits individual carriages to be quickly and easily shifted and also permits an entire cutting pattern set up to be shifted as a unit. The linear positioning apparatus taught by U.S. Pat. No. 4,170,159 is expensive to manufacture and to maintain and is also complex in operation.
When a cutting pattern is desired to be changed it is oftentimes not necessary to have the capability to shift the position of each cutting assembly carriage independently or individually, without returning each carriage to a fixed reference or home/base position. This is primarily because the time which is required to return all of the carriages to the home position, then to set up a new cutting pattern, and finally, to move the carriages into position to perform the desired/selected cutting pattern, is less than the time that is available before cutting must be resumed. Therefore, the apparatus taught in U.S. Pat. No. 4,170,159 is unnecessarily complex and expensive to build, operate and maintain when the time frame parameters of the cutting operation do not require that the cutting assembly carriages be independently movable, as above-discussed. McNally teaches a friction clamping means comprising brass wear pads biased by spring steel members to continually engage the actuating rod. The wear pads are susceptible to wear-out, thereby necessitating replacement of the worn-out pads. Further, detection of the worn out condition of the wear pads may be difficult and even slightly worn pads may create the problem of slippage or undesired relative movement of the associated carriage and the actuating or positioning rod, which could cause the carriage(s) to be mispositioned or misaligned for the desired cutting pattern. Further, the method taught by McNally for positioning the carriages, is to utilize a programmed computer controller to move the actuating rod and then disengage each carriage therefrom by applying the locking means to hold the associated carriage to the fixed guide rail at a preselected position across the work surface in accordance with the cutting pattern established in the computer program. When a change in the cutting pattern is to be effected, the holding means associated with any one or more of the carriages which must be shifted to effect the modified cutting pattern, is released, thereby enabling the affected carriage(s) to move unitarily with the actuating rod until its new position is reached, at which juncture, the holding means is again actuated to hold the associated carriage to the guide rail at the new position. All of the above events are controlled by the computer controller pursuant to programmed instructions. The complexity of the computer controller and program logic is much greater than a positioning method which does not have independently movable carriages.
It would be advantageous and desirable to have a linear positioning system which eliminates the drawbacks and shortcomings of the apparatus of U.S. Pat. Nos. 3,834,258 and 4,170,159.